Dopaminergic Actions of d-Amphetamine on Schedule-Induced Polydipsia in Rats

Abstract

Schedule-induced polydipsia in rats was developed by means of a fixed-time 60-s schedule of food presentation. The acute administration of d-amphetamine sulfate (0.1–3.0 mg/kg) produced a dose-dependent decrease in the rate of licking. d-Amphetamine shifted to the left the temporal distribution of adjunctive drinking within interfood intervals. Dopaminergic antagonists SCH23390 ([R(+)-7-chloro-8-hydroxy-3-methyl-1-phenyl-2,3,4,5-tetrahydro- 1H-3-benzazepine hydrochloride], 0.001–0.01 mg/kg), eticlopride (0.001–0.03 mg/kg), and flupenthixol (0.03–0.3 mg/kg) also produced dose-dependent decreases in licks per minute but did not alter the temporal distribution of adjunctive behavior. Selective doses of dopaminergic antagonists further suppressed licking rates when combined with d-amphetamine, 1.0 mg/kg, but an antagonism could be observed on the temporal distribution after the administration of SCH23390 (0.01 mg/kg) or flupenthixol (0.1 mg/kg). The dopaminergic agonists SKF38393 ([R(+)-1-phenyl-7,8-dihydroxy-2,3,4,5-tetrahydro-1H-3-bezazepine hydrochloride]; 1.0–10.0 mg/kg) and quinpirole (0.003–0.03 mg/kg) produced a dose-dependent decrease in the rate of licking, and when combined with d-amphetamine, additive-like suppressive effects were found. These results suggest a dopaminergic selectivity for the effects of d-amphetamine on the temporal distribution of schedule-induced polydipsia.